Hi,
Mes couleurs préférées, ce sont le bleu et le vert.
Mes desserts préférés, ce sont la tarte aux pommes et la glace à la vanille.
I'm sure these are correct, but they kind of sound wrong through hypercorrection. Grammatically speaking, you need the plural, but saying
"Ce sont le..." or
"Ce sont la..." isn't exactly idiomatic. I'd probably avoid saying it despite the fact I could defend the usage.
I don't think English is very different on this point. You would most likely say
There is a cat and a dog (even though there are several animals), but
There are cats and dogs.
"Ce sont" would be fine if there was a
plural noun (as opposed to two singular nouns) instead.
Mes desserts préférés, ce sont les tartes.
I would probably
write "Les desserts que je préfère sont la tarte aux pommes et la glace à la vanille", but
say "Les desserts que je préfère, c'est la tarte aux pommes et la glace à la vanille".